Expression of genetic information in eucaryotic cells is regulated at the levels of transcription into mRNA, mRNA processing, translation to protein and posttranslational processing. The regulation at the transcription level most strongly influences the expression of genetic information. A promoter which controls transcription is found on the 5' side of genes transcribed by RNA polymerase II and sometimes enhancers, which regulate promoter activity were also found. With the recent discovery of nuclear factors that recognize and bind to specific nucleotide sequences in the promoter and enhancers, it has become evident that the activities of promoter and also enhancers are mediated by the binding of these factors.
Of such factors, for example, studies on proteins which interact with TATA box, CAAT box, or GC box for the stimulation of transcription of RNA polymerase have been undertaken. Cloning of cDNA of CAAT-binding and GC-binding factors has already been accomplished.
Furthermore, factors that bind to enhancers have been investigated and cDNA clones of several transcription factors have been successfully isolated: for example, octamer transcription factor-2 (OTF-2), a B-cell lineage specific factor, that binds to immunoglobulin .kappa.-chain gene enhancer [Michael et al.: Nature, 336, 544-551, (1988)] and OTF-1, which recognizes the same nucleotide sequence and was found ubiquitously in many tissues [R. A. Sturm, G. Das and W. Herr: Gene & Development, 2, 1852 (1988)].
In human .alpha.-fetoprotein gene, presence of an enhancer at 3.5 kb on the upstream of transcription start point has been confirmed. A factor that binds to this enhancer has been discovered and named AFP-1 [Sawadaishi et al.: Molecular and Cellular Biology, 8, 5179-5187 (1988)].
However, the structure and physiological properties of AFP-1, and on the gene which codes for AFP-1 has not been elucidated.